I do not know where you are from, so first a word about units. In EU the buoyancy is given in SI-unit Newtons (N) which is the unit of force.

If you are using impact vest their buoyancy can be something like 20N, but they are not buoyancy devices but they do float a little. One local guy needed to ditch his helmet when he was in trouble with wetsuit & impact vest on. Buoyancy category officially starts from 50N and vest/PFD is officially stamped with CE-marking. Some impact vest vendors has 50N vests/PFDs on their selection.

If kiting specific accessories are not enough what you are looking for in terms of buoyancy you could look white water PFDs.

In kiting at home location I (heavy boy) use wet suit accompanied with 50N white water paddler vest just because I already have those on my garage. White water PFDs are made for high torso/arm maneuverability. But WW PFD are not compatible with waist harness but I use them with North Performer which gives fairly high hook position. There are also 100N white water vests but I use those only at river with a kayak.

But if you are looking something with waist harness you could be limited to only one or two commercial possibilities. Or DIY white water paddler PFD without Zipper and make a hole for hook. Or glue more low density buoyancy material to your impact vest but you need a lot of plates because it is question of density and volume how much water is "pushed" away when submerged like Archimedes did.